It is proposed to study in trained, unanesthetized dogs serving as their own controls, the early and late effects of moderate and severe experimental hypertension on mean arterial pressure (MAP), cardiac output (CO) and total peripheral resistance (TPR), fluid and electrolyte balance, plasma renin activity (PRA), plasma renin concentration (PRC), renin substrate concentration (RSC), plasma aldosterone concentration (PA) and urinary ADH. These same variables will be studied during the decrease of elevated arterial pressure following release of the constricting device. Hypertension will be studied in both the one and two-kidney models of unilateral renovascular hypertension. The effects of the angiotensin II antagonist, Sar l 1le8 angiotensin II, will be studied at various stages of hypertension.